As a result of the increasing electrification of the drive train of modern motor vehicles, electrical or electronic components such as, for example, semiconductors, in particular, in the form of switching elements such as transistors are used to an increasing extent. These are exposed to the inhospitable external conditions of the engine compartment, for example, passive temperature lifts. Passive temperature lifts are created by the waste heat of the internal combustion engine heating the engine compartment while the vehicle is driving.
A particularly high load acts on electronic components of the converter of the electric machine in such motor vehicles, which experience additional loads from active temperature lifts due to the self-heating at high current. Large current amplitudes are typically reached during motor-driven boost processes and generator-driven recuperation processes (in vehicles having correspondingly operable electric machines). The electronic components of the converter are functionally critical components, since their failure results in a non-functionality of the complete electric machine.
The service life of electronic components and, thus, that of the converter of the electric machine as well, is a function essentially of the cyclization with active and passive temperature changes, since in assembly and connection technology materials having different expansion coefficients are used. These different expansion coefficients (so-called thermal mismatch) result in mechanical stresses during a thermal heating or cooling of the assembly and connection technology.
Since the number and amplitude of boost and recuperation processes depend greatly on the application, i.e., among other things, on the driving behavior of the driver (aggressive, defensive) and/or the traffic situations, in which a corresponding motor vehicle is predominantly moved (city traffic, freeway), the configuration of the electronic components in the converter represents a technical challenge.
In order to avoid a premature and uncontrolled failure of electrical or electronic components, methods for estimating their residual service life may be used. In such methods, the residual service life is determined with the aid of a thermal model and by storing temperature lifts.
A method for adapting a residual service life of a semiconductor in a motor vehicle is discussed, for example, in DE 10 2013 203 661 A1. For this purpose, a load influencing factor is reduced when a deviation is detected of an actual load from a setpoint load of the semiconductor. A more precise description of the initiated measures is not given, however.
The need exists, therefore, for improved ways of operating electrified motor vehicles, which include corresponding electrical or electronic components in their vehicle electrical system, and with the aid of which a more reliable operation is facilitated with no unexpected failures and losses of comfort.